Impregnation process



United States Patent 1 2,931,737 IMPREGNATION PROCESS Jesse Thornton,Leeds, England, assignor to Hicksons Timber impregnation Co. (G.B.)Limited, Castleford,

England, a British company No Drawing. Application April 4, 1958 SerialNo. 726,316 Claims priority, application Great Britain July 30, 1957 4Claims. (Q1. 117- 116) This invention'is concerned withimprovements inor relating to impregnation processes, and is more particularlyconcerned with the. impregnation of fibreboard materials with liquids,such as aqueous solutions containing, for example, fire-retardantsand/orpreservatives, and/or with aqueous solutions of resins capable ofimparting dimensional stability.

' By the term fibre-board as used herein we means.

any board which has been manufactured by compression of comrninutedcellulose, such as insulation board and wall board and also includessuch materials as cardboard which are made under light compresison aswell as the more solid type of board. The term does not, however,include fibre-boards which are of such a solid nature that it is notfeasible to impregnate them, for example such boards as have a hardnesscomparable to that of metal.

facturing process; furthermore the amount ofdmpregnant which isincorporated in'the fibre-board cannot be controlled accurately and, inaddition, there is considerable waste of impregnant.

It is also virtually impossible to impregnate fibre-board by merelyimmersing the manufactured board in an impregnant solution as the boardbecomes virtually impossible to handle in the wet state because itbecomes soft.

Various processes are now well-known for impregnation of timber with,for example, preservative solutions and examples of such processesinclude variouspressure/ vacuum impregnation processes. Timber, however,has a continuous cellular structure and consists substantially of a massof inter-connected cells. Fibre-boards with which the present inventionis concerned have, however, a discontinuous structure and thus theproblem of their impregnation should differ radically from theimpregnation of timber. We have, however, found that one of theimpregnation processes developed for treating timber (and dependent onthe continuous cellular structure thereof), namely the Rueping process,is capable of adaptation to the successful impregnation of fibre-boarddespite the discontinuous structure of the latter. 7

:The Rueping process for the treatment of timber consists basically inforcing air or other gas under pressure into the timber to beimpregnated and then forcing the impregnant liquid into the timber at ahigher pressure than that at which the air or other gas was introduced.

vAfter a certain time the pressure is released and, if desired, a vacuumis applied to the timber when a large quantity of the impregnant isforced out of the timber by the gas contained therein under pressure. Bycontrolling theinitial gas pressure and the pressure at which the liquidis forced into the timber, and, if desired,'the'time 2,931,731 PatentedApr. 5, 19$!) 'ice 2 of impregnation, the amount of impregnantintroduced into the timber can be controlled as well as the depth ofimpregnation.

According to the invention, therefore, we provide a process for the.impregnation of fibre-board with an impregnant liquid in which thefibre-board is subjected in a pressure vessel to an initial gas,preferably air, pressure, impregnant liquid is then introduced into thepressure vessel under a pressure greater than that of the initial gaspressure to force the impregnant liquid into the fibreboard against theinitial gas pressure to the desired degree of impregnation after whichthe liquid pressure is released.

A further measure of control of the amount of impregnation'may besecured by variation of the time within which said liquid pressure isapplied.

he pro ss a cording o the invent on is conveniently carried out forexample using a conventional yacuuml pr ssu mpre ati p a t s us fo h mprnation of timber. Other methods of operation can of course be used.

By the process according to the-invention it is possible to impregnatefibre-board to, any desired degree and to achieve any desired depth ofimpregnatiom- This represents a considerable advance in the art asfibre-board.

is very absorbent and immersion in liquid for very short periods resultsin a very high volumetric absorption. line, if reference is made to thetable set out below it will be seen that the absorption in litres percubic 'rnetre of fibre-board of impregnant is very high even after'onlya few minutes immersion. i

Duration of Immersion Absorption in Litres/m3 Min s. Secs.

catamaran- 0 em- OOQOOOO! cording to the invention, however, it ispossible to achieve to been possible.

Thus if reference is made to the table set out below it will be seenthat the absorption of impregnant in litres per cubic metre offibre-board can be controlled tea may fine degree. i v

control of the impregnation process which has not hither- TREATMENTCYCLE Initial Air Solution Vacuum Pressure 1 Pressure Absorption,Exlairmple l I g v H 'Litres/mz! 0. .3sam les Kg] Mins. KgJ Mins. mm!Mins. cm, cm. Hg

i "is. l 1.41 10 1. 41 3O 72. 3 10 2.82 30 ii) From the above table itwill be apparent that it is possible to control accurately theabsorption of the impregnant within the range of about 65-500litres/m3", the latter quantity of impregnant being in generalsufficient to impart substantially complete fire-retardancy to thefibre-board being treated Whilst a quantity of about 65 litres/m. wouldimpart a considerable fire-retardancy to the surface of the fibre-board.It should be noted in this connection that it may often only benecessary to impart a fire-retardancy-to the surface of fibre-board andthat by the process according to the invention it is possible to controlthe. depth of impregnation to a considerable degree. Thus, in Example 1of the above table the fibreboard is impregnated to a depth of,approximately 3.2 mm., leaving the centre core of the board dry and freefrom fibre-retardant.

The process according to the invention gives the best results whenoperated within certain pressure and time limits which are set out inthe table below.

achieve control of the impregnation process. The process according tothe invention is, of course, not restricted to the use of aqueoussolutions but could equally well be applied to non-aqueous solutions. Inpractice it is very often preferable to impregnate with aqueoussolutions thus avoiding use of expensive solvents so that the presentinvention particularly includes the use of aqueous impregnant solutions.

The process according to the invention can clearly be applied to theimpregnation of fibre-board with any desired solution and is notrestricted to imparting fireretardancy thereto. Thus the solution usedfor impregnation may contain preservatives as well as or in place offire-retardants; they may also contain resins for imparting dimensionalstability. In fact, it may often be desirable to incorporate bothfire-retardants and preservatives into the fibre-board being treated aswell as resins for imparting dimensional stability.

After the fibre-board has been subjected to the im As will be seen fromthe above table, it is preferred that the initial air pressure be withinthe range of 1-3 kg./cm. and that it should be maintained for 5-20minutes. Preferably the pressure of the impregnant liquid introducedafter the air has been introduced is within the range of 1.5-7 kglcm.and such pressure should first be maintained for 10-60 minutes. Finally,it is preferred that a vacuum of 250-740 mm./Hg be applied after theimpregnant liquid has been introduced, such vacuum being maintained fora time within the range of from 5-60 minutes.

The process according to theinvention can be used for the impregnationof fibre-board with any desired liquids. In practice, such liquids willoften be aqueous solutions containing for example fire-retardant saltsor preservative salts or aqueous solutions of resins capable ofproducing dimensional stability in the fibre-board. Where aqueous saltsolutions are used the concentrations employed canvary. as desired andin the case of fireretardant compositions may, for example, contain from.5-30, preferably 10-20% of fire-retardant substances.

tions. This is because no advantage would normally be gained by usingthe Rueping process for the impregnation of timber using aqueoussolutions as other methods of'impregnation are equally applicable. It isonly where it is desired to conserve the solvents containing theimpregnant as much as possible that one applies the Rueping processbecause in this process a large quantity of the impregnant is forced outunder pressure after impregnation has taken place. Thus, it is only inthe case where recovery is important that the Rueping process has beenapplied.

In the process according to the invention, however, it is only byapplying the Rueping process that one can Initial air pressure 2.12kg./cm.=, 10 mins. Solution pressure 8.18 kg./cm., 30 mins. Vacuum 625mm. Hg, 15 mins. Absorption 190 litres/n13.

Fire retardant solution M o n o ammonium dihydrogcn phosphate, ammoniumsulphate and borax.

Solution strength 15%.

Net dry salt retention 40.0 kgJmP.

Example 2 1.89 CM. THICK FIBRE INSULATION BOARD TILES Treatment cycle:

, Initial air pressure- 2.82 k n/cm). 10 mins. Solution pressure 4.23ken/cm). 35 mins. Initial vacuum 609 mm. Hg. 12 mins. Absorption 330litres/m3. Fire retardant solution M o n o ammonium dihydrogenphosphate, ammonium sulphate and borax. Solution strength 15 Net drysalt retention--. 48.0 kg./m..

Example 3 1.27 CM. FIBRE INSULATION BOARD Treatment cycle:

, Initial air pressure"--. 2.12 Ira/cm}, 10 mins. Solution pressure 2.82kgjcmfi. 30 mins. Absorption litres/m3.

SOlIltlOll Disodium arsenate, sodium fluoride, sodium chromate. Solutionstrength Net dry salt retention--. 8.0 kgJmfl.

I claim: 1. A process for the controlled impregnation with an impregnantliquid of a highly absorbent fibre-board of compressed comminutedcellulose having a density not exceeding 720 kg./m. comprisingsubjecting the fibreboard in a pressure vessel to an initialsuperatmospheric gas pressure not greater than 3 kg./cm. for from 5-20minutes, introducing impregnant liquid into the pressure vessel under apressure greater than that of the initial gas pressure but not greaterthan 7 kg./cm. for from 10-60 minutes to force the impregnant liquidinto the fibre-board against the initial gas pressure to obtain arelatively high concentration of impregnant in the outer portions ofsaid fibre-board while leaving the centre portion of said fibre-boardsubstantially free of impregnant and releasing the liquid pressure.

2. A process as claimed in claim 1 in which a vacuum of from 254-735 mm.Hg is applied to remove excess impregnant liquid after release of theliquid pressure.

3. A process as claimed in claim 2 in which the vacuum is applied for aperiod of from 5-60 minutes.

4. A process as claimed in claim 1 in which said impregnant liquid is anaqueous solution.

Wheaton Ian. 20, 1925 Coolidge Oct. 6, 1925

1. A PROCESS FOR THE CONTROLLED IMPREGNATION WITH AN IMPREGNANT LIQUIDOF A HIGHLY ABSORBENT FIBRE-BOARD OF COMPRESSED COMMINUTED CELLULOSEHAVING A DENSITY NOT EXCEEDING 720 KG./M.3, COMPRISING SUBJECTING THEFIBREBOARD IN A PRESSURE VESSEL TO AN INITIAL SUPERATMOSPHERIC GASPRESSURE NOT GREATER THAN 3 KG./CM.2 FOR FROM 5-20 MINUTES, INTRODUCINGIMPREGNANT LIQUID INTO THE PRESSURE VESSEL UNDER A PRESSURE GREATER THANTHAT OF THE INITIAL GAS PRESSURE BUT NOT GREATER THAN THAT OF THEINITIAL 10-60 MINUTES TO FORCE THE IMPREGNANT LIQUID INTO THEFIBRE-BOARD AGAINST THE INITIAL GAS PRESSURE TO OBTAIN A RELATIVELY HIGHCONCENTRATION OF IMPREGNANT IN THE OUTER PORTIONS OF SAID FIBRE-BOARDWHILE LEAVING THE CENTRE PORTION OF SAID FIBRE-BOARD SUBSTANTIALLY FREEOF IMPREGNANT AND RELEASING THE LIQUID PRESSURE.